1. Field of the Invention
The present invention relates generally to cameras of the motor-drive type that includes an automatic exposure control apparatus, an automatic focus adjustment apparatus, a lens shutter and a TTL viewfinder. More specifically, the invention relates to a camera having an improved automatic focus adjustment apparatus which includes an improved motor drive circuit for driving a film, an improved autofocus system and an improved lens position setting system which functions when autofocus is impossible.
2. Description of Related Art:
It has been proposed to provide a camera which has both a lens shutter and a TTL viewfinder.
Such a camera is disclosed in Japanese Patent Publication No. sho 56-5975. This prior art camera is arranged such that a film is manually wound and rewound.
It has also been proposed to provide cameras in which both shutter charging and film winding and rewinding are motorized. Cameras whose focus can be automatically adjusted are also available.
However, if such a camera having a lens shutter and a TTL viewfinder is to be combined with an automatic focus adjustment apparatus and a plurality of motors for driving the autofocus apparatus and the mechanism of each portion of the camera, various problems will be encountered in connection with the capacity of the power source, the distribution of the output of each motor and the like. Also, like the viewfinder of a TTL-type SLR cameras, it is undesirable that, while a user is taking photographs using the above camera having a lens shutter and a TTL viewfinder, the visual field in the viewfinder be blocked for a long time.
Second, if, for example, a subject has a low contrast, a conventional type of autofocus camera may be unable to measure the distance. To cope with this problem, it has been proposed to provide a camera arranged to issue a warning of its inability to measure distance or a camera arranged to set its photographing lens to a predetermined distance. However, these conventional cameras have the problem that, if it is desired to take a photograph in a situation in which distance measurement is impossible, the photographing lens cannot be set to a distance suitable for the brightness of a subject since the photographing lens is fixed to a predetermined distance in such a situation.
Third, in general, a conventional type of autofocus camera is arranged so that its photographing lens will not accidentally move and so that, at the time of photography, it can be switched to a movable state by a switching mechanism. Also, if such an autofocus camera adopts a triangulation system or a coding system in which the distance of the photographing lens can be read using a value representing the movement of the photographing lens which movement is coded with reference to infinity or the closest distance, flash photography can be carried out utilizing the distance represented by such a code.
However, in a phase-difference distance measurement type of autofocus camera which includes no switching mechanism between autofocus and manual focusing, a photographing lens movable independently of the autofocus system, and a photo-interrupter used for measuring the amount of movement of the photographing lens, if the photographing lens is moved accidentally, it is possible to read out how much the photographing lens is spaced from an in-focus position but impossible to read a subject-to-camera distance.
Accordingly, when it is desired to use such a camera to carry out flash photography in a dark place or flashmatic fill-in flash photography, it is impossible to automatically input information upon the distance to a subject and therefore to execute automatically controlled flash photography.
Fourth, in general, the amount of protrusion of a lens barrel is made large when a subject to be photographed is located at a short distance, but is made small when the subject is located at a long distance. Also, in the case of a typical zoom lens, the amount of protrusion of its lens barrel is larger at a wide-angle (WIDE) position than at a telephoto (TELE) position. Therefore, it is preferable that the above motor drive-type autofocus camera having a lens shutter and a TTL viewfinder be arranged such that when the camera is not in use, the lens barrel is reset to the most inward position, for example, an initial position.
It is therefore a first object of the present invention to provide an autofocus camera in which it is possible to substantially shorten the period required for the visual field in the viewfinder to be blocked, in which a sequence of photographic operations can be executed rapidly and with reduced electrical power, and which has a reduced size.
It is a second object of the present invention to provide an autofocus camera which, if distance measurement is impossible and a subject is bright, can set its photographing lens to one of several predetermined long distances or to infinity since a bright subject such as a mountain, sea, sky or clouds is commonly located at a long distance from the camera, and which, if distance measurement is impossible and a subject is dark, can fix the photographing lens to one of several predetermined short distances since a dark subject is often photographed using a flash.
It is a third object of the present invention to provide an autofocus camera which enables automatically controlled flash photography by automatically temporarily moving a photographing lens to infinity or the closest distance prior to effecting automatic adjustment of focus and measuring the distance between the subject and the camera with reference to infinity or the closest distance to use the measured value as the distance information for flash photography.
It is a fourth object of the present invention to solve various other problems involved in an autofocus camera, particularly those connected with the amount of protrusion of a lens barrel of a zoom lens for use in the autofocus camera.